Replacing spherical bearings at the wing root? (Grob Astir CS)

The spherical bearings that mate to the spar spigots in my Astir CS are binding when turned to larger angles.
When rigging the wings, a slight misalignment of the spigot jams the bearing and any further progress becomes impossible until you pull the wing out and unjam the bearing using a wooden dowel (it wouldn't turn by hand once jammed).
This makes putting wings together a royal PITA.

Closer look revealed that the far side of the "outer race", is worn out and pitted and likely is the culprit.

The bearing in question is SKF GE 20 ES, which seems to be easily available.

It appears to be pressed in into a metal sleeve that is bonded into the wing root, and four areas are punched in to further lock it in place.

We couldn't find anybody local who would readily know the process of replacement of that bearing.

Is anybody familiar with maintenace/replacement of these?

- Is that bearing replaceable? It seems like the only way to extract it is to slide-hammer it out and tap a new one in.
- How critical is it? I assume that it radially transfers the entire load of the wing

-Movses

On Tuesday, March 3, 2015 at 3:47:42 PM UTC-5, Movses wrote:
The spherical bearings that mate to the spar spigots in my Astir CS are binding when turned to larger angles.
When rigging the wings, a slight misalignment of the spigot jams the bearing and any further progress becomes impossible until you pull the wing out and unjam the bearing using a wooden dowel (it wouldn't turn by hand once jammed).
This makes putting wings together a royal PITA.

Closer look revealed that the far side of the "outer race", is worn out and pitted and likely is the culprit.

The bearing in question is SKF GE 20 ES, which seems to be easily available.

It appears to be pressed in into a metal sleeve that is bonded into the wing root, and four areas are punched in to further lock it in place.

We couldn't find anybody local who would readily know the process of replacement of that bearing.

Is anybody familiar with maintenace/replacement of these?

- Is that bearing replaceable? It seems like the only way to extract it is to slide-hammer it out and tap a new one in.
- How critical is it? I assume that it radially transfers the entire load of the wing

-Movses

Where are you located? There are a few people in the US who know quite a bit about these birds.

Erik Mann
Former Astir CS owner

I would say LTB Lindner would have all the details. They are Type
Certificate Holder for the Astir CS I believe. Changed a fair few myself,
not a big hassle. There's a clearance to be observed in most Grobs wings
attachments (see manual) regarding wear limits. Often overlooked. Check
your other fittings for that too whilst you are at it.

At 20:47 03 March 2015, Movses wrote:
The spherical bearings that mate to the spar spigots in my Astir CS are
binding when turned to larger angles.
When rigging the wings, a slight misalignment of the spigot jams the
bearing and any further progress becomes impossible until you pull the
wing
out and unjam the bearing using a wooden dowel (it wouldn't turn by hand
once jammed).
This makes putting wings together a royal PITA.

Closer look revealed that the far side of the "outer race", is worn out
and
pitted and likely is the culprit.

The bearing in question is SKF GE 20 ES, which seems to be easily
available.

It appears to be pressed in into a metal sleeve that is bonded into the
wing root, and four areas are punched in to further lock it in place.

We couldn't find anybody local who would readily know the process of
replacement of that bearing.

Is anybody familiar with maintenace/replacement of these?

- Is that bearing replaceable? It seems like the only way to extract it
is
to slide-hammer it out and tap a new one in.
- How critical is it? I assume that it radially transfers the entire load
of the wing

-Movses

On Tuesday, March 3, 2015 at 1:24:11 PM UTC-8, Papa3 wrote:
On Tuesday, March 3, 2015 at 3:47:42 PM UTC-5, Movses wrote:
The spherical bearings that mate to the spar spigots in my Astir CS are binding when turned to larger angles.
When rigging the wings, a slight misalignment of the spigot jams the bearing and any further progress becomes impossible until you pull the wing out and unjam the bearing using a wooden dowel (it wouldn't turn by hand once jammed).
This makes putting wings together a royal PITA.

Closer look revealed that the far side of the "outer race", is worn out and pitted and likely is the culprit.

The bearing in question is SKF GE 20 ES, which seems to be easily available.

It appears to be pressed in into a metal sleeve that is bonded into the wing root, and four areas are punched in to further lock it in place.

We couldn't find anybody local who would readily know the process of replacement of that bearing.

Is anybody familiar with maintenace/replacement of these?

- Is that bearing replaceable? It seems like the only way to extract it is to slide-hammer it out and tap a new one in.
- How critical is it? I assume that it radially transfers the entire load of the wing

-Movses

Where are you located? There are a few people in the US who know quite a bit about these birds.

Erik Mann
Former Astir CS owner

Seattle, WA area

On Tuesday, March 3, 2015 at 1:45:06 PM UTC-8, Eric Munk wrote:
I would say LTB Lindner would have all the details. They are Type
Certificate Holder for the Astir CS I believe. Changed a fair few myself,
not a big hassle. There's a clearance to be observed in most Grobs wings
attachments (see manual) regarding wear limits. Often overlooked. Check
your other fittings for that too whilst you are at it.

At 20:47 03 March 2015, Movses wrote:
The spherical bearings that mate to the spar spigots in my Astir CS are
binding when turned to larger angles.
When rigging the wings, a slight misalignment of the spigot jams the
bearing and any further progress becomes impossible until you pull the
wing
out and unjam the bearing using a wooden dowel (it wouldn't turn by hand
once jammed).
This makes putting wings together a royal PITA.

Closer look revealed that the far side of the "outer race", is worn out
and
pitted and likely is the culprit.

The bearing in question is SKF GE 20 ES, which seems to be easily
available.

It appears to be pressed in into a metal sleeve that is bonded into the
wing root, and four areas are punched in to further lock it in place.

We couldn't find anybody local who would readily know the process of
replacement of that bearing.

Is anybody familiar with maintenace/replacement of these?

- Is that bearing replaceable? It seems like the only way to extract it
is
to slide-hammer it out and tap a new one in.
- How critical is it? I assume that it radially transfers the entire load
of the wing

-Movses



Wrote to Lindner and heard back. They're saying they never had to deal with replacement and basically don't know.

The root rib bearing spinning during assembly is something all Grobs have in common. With the ship assembled, I would check for any vertical movement at wing tip (with the other wing tip on a stand). Pick up wing tip with about 25 pound force and check for slop. You can feel any movement. If the wings are tight, I wouldn't change the bearings. You could consider gooping up the bearing to keep it in proper alignment for next assembly, something that would keep the bearing from spinning and still allow slight movement. The heavy wax used in a toilet ring might do the job.
Hope this helps,
JJ

On Wednesday, March 4, 2015 at 7:23:03 PM UTC-5, JJ Sinclair wrote:
The root rib bearing spinning during assembly is something all Grobs have in common. With the ship assembled, I would check for any vertical movement at wing tip (with the other wing tip on a stand). Pick up wing tip with about 25 pound force and check for slop. You can feel any movement. If the wings are tight, I wouldn't change the bearings. You could consider gooping up the bearing to keep it in proper alignment for next assembly, something that would keep the bearing from spinning and still allow slight movement. The heavy wax used in a toilet ring might do the job.
Hope this helps,
JJ

Reread the 1st post, they have an issue of NOT being able to align the "ball" easily.
;-)

Movses....... I would try using a bar (maybe brass or aluminum) inside the "ball" and working it around while spraying some WD-40, PB Blaster, Kroil, etc. on the "ball - socket joint". You will likely wash out some rust and maybe smooth some rough spots.
I would just do enough to get it "free" as you don't want it to go too loose, then you're into what JJ was referring to.
Wipe everything down to get it clean & dry once the ball is free.
Keep a bit of a light oil on the OD of the ball once it's free.

PS, I would use plastic sheeting or similar to keep whatever spray you use from soaking into the rest of the wing root.

When I owned my Astir, I machined a delran rod of the appropriate ID to use for the purpose of aligning the ball sockets at the start of assembly. Much cleaner than using my hands.

Secondly, you do want to make sure the outside of the ball is well lubed; I used a synthetic grease (Superlube). Keep the interface with the socket well packed.

Third, the trick is to have everything carefully aligned beforehand. Fuselage exactly vertical. First wing inserted exactly at the right dihedral. Slowly and carefully insert second wing using a reference line on the first wing (i.e when the glider is assembled, use a black sharpie to draw a line along the first spar shows how the second spar lines up). If it's all lined up, the ship goes together in seconds.

As far as answering the original question (wear limits and such), if Linder wasn't aware of any, then there's probably none published. Robert Mudd is a good source of info.

PM me if you want more thoughts.

Erik Mann

On Thursday, March 5, 2015 at 8:42:18 AM UTC-5, Charlie M. (UH & 002 owner/pilot) wrote:
On Wednesday, March 4, 2015 at 7:23:03 PM UTC-5, JJ Sinclair wrote:
The root rib bearing spinning during assembly is something all Grobs have in common. With the ship assembled, I would check for any vertical movement at wing tip (with the other wing tip on a stand). Pick up wing tip with about 25 pound force and check for slop. You can feel any movement. If the wings are tight, I wouldn't change the bearings. You could consider gooping up the bearing to keep it in proper alignment for next assembly, something that would keep the bearing from spinning and still allow slight movement.. The heavy wax used in a toilet ring might do the job.
Hope this helps,
JJ

Reread the 1st post, they have an issue of NOT being able to align the "ball" easily.
;-)

Movses....... I would try using a bar (maybe brass or aluminum) inside the "ball" and working it around while spraying some WD-40, PB Blaster, Kroil, etc. on the "ball - socket joint". You will likely wash out some rust and maybe smooth some rough spots.
I would just do enough to get it "free" as you don't want it to go too loose, then you're into what JJ was referring to.
Wipe everything down to get it clean & dry once the ball is free.
Keep a bit of a light oil on the OD of the ball once it's free.

PS, I would use plastic sheeting or similar to keep whatever spray you use from soaking into the rest of the wing root.

HI

When I owned a Astir CS some years ago I replaced those bearings. At the time I felt that they had too much free play or slop in them.
I made a device fitted into the centre of the bearing and then expanded out to grip the internal grove inside the bearing. I then had a outer cup which that had an internal bore just greater than the outer of the bearing. The system was such that by screwing up a nut on the outside it would pull the bearing out whilst pushing on the outer mounting region. I have still have the device in my shed.
Those bearings take the bending moment of the wings into each other.
In service the only time those bearings move would be during rigging and hence it should never be to large angles. Free play in the bearings would really only be noticed in load reversals. Binding in those bearings would only be a problem if they were causing difficulty during rigging.

As Papa3 mentions the secret in rigging is getting the wing angles correct. I never worried about lining up the bearings just made sure that the wing angles were correct and presto it worked for me.

johnorto at gmail dot com

On Tuesday, 3 March 2015 20:47:42 UTC, Movses wrote:
The spherical bearings that mate to the spar spigots in my Astir CS are binding when turned to larger angles.
When rigging the wings, a slight misalignment of the spigot jams the bearing and any further progress becomes impossible until you pull the wing out and unjam the bearing using a wooden dowel (it wouldn't turn by hand once jammed).
This makes putting wings together a royal PITA.

Closer look revealed that the far side of the "outer race", is worn out and pitted and likely is the culprit.

The bearing in question is SKF GE 20 ES, which seems to be easily available.

It appears to be pressed in into a metal sleeve that is bonded into the wing root, and four areas are punched in to further lock it in place.

We couldn't find anybody local who would readily know the process of replacement of that bearing.

Is anybody familiar with maintenace/replacement of these?

- Is that bearing replaceable? It seems like the only way to extract it is to slide-hammer it out and tap a new one in.
- How critical is it? I assume that it radially transfers the entire load of the wing

-Movses

I had precisely the problem you describe, in all its aspects, with my G109B.. It was caused during rigging by striking the bearing when trying to insert the main spar spigot. The engineer removed the whole unit from the center of the fuselage using a balk of timber and a heavy hammer, and replaced it with a new one (the bearings on both sides had this problem).

I have been much more careful since then, and offer up the spigot very slowly.